A novel robotic platform for aerial manipulation using quadrotors as rotating thrust generators

We propose a novel robotic platform for aerial op- eration and manipulation, a spherically connected multiquadro- tor (SmQ) platform, which consists of a rigid frame and multiple quadrotors that are connected to the frame via passive spherical joints and act as distributed rotating thrust generators to collec- tively propel the frame by adjusting their attitude and thrust force. Depending on the number of quadrotors and their configuration, this SmQ platform can fully (or partially) overcome the issues of underactuation of the standard multirotor drones for aerial oper- ation/manipulation (e.g., body-tilting with sideway gust/force, dy- namic interaction hard to attain, complicated arm–drone integra- tion, etc.). We present the dynamics modeling of this SmQ platform system and establish the condition for its full actuation in SE(3). We also show how to address limited range of spherical joints and rotor saturations as a constrained optimization problem by notic- ing the similarity with the multifingered grasping problem under the friction-cone constraint. We then design and analyze feedback control laws for the S3Q and S2Q systems as a combination of high-level Lyapunov control design and low-level constrained opti- mization and show that the (fully actuated) S3Q system can assume any trajectory in SE(3), whereas the S2Q system in 3 × S 2 with its unactuated dynamics is still internally stable. Experiments are also performed to show the efficacy of the theory